The invention relates to an arrangement for monitoring and presenting the status of an electrolytic process such as an metal electrorefining process or an metal electrowinning process in an electrolytic cell according to the preamble of claim 1.
The invention also relates to an arrangement for monitoring and presenting the status of an electrolytic process such as an metal electrorefining process or an metal electrowinning process in an electrolytic cell according to the preamble of claim 16.
In a process for electrorefining or for electrowinning of metals, the desired metal is precipitated on the surface of an electrode, i.e. a cathode. The processing is carried out by electric current in an electrolytic cell, and in the liquid, i.e. electrolyte contained in the cell, there are immersed in turn a number of sheet-like anodes and sheet-like cathodes made of an electroconductive material. The desired metal is precipitated on the cathode either so that in the electrolytic treatment, there is used a soluble anode made of the same metal as the metal to be precipitated, or there is used a non-soluble anode. A soluble anode is used for example in copper electrorefining, and a non-soluble anode is used for example in nickel or zinc electrowinning.
In the electrolytic purification of copper, the impure copper, i.e. so-called anode copper, is dissolved by means of electric current, and the dissolved copper is reduced on the cathode sheet as very pure copper, so-called cathode copper. The employed electrolyte is a sulfuric acid based copper sulfate solution. In the beginning of the process, the employed cathode sheet is a copper seed plate or a so-called permanent cathode that can be made of acid-proof steel or titanium. The employed power source in electrolysis is one or several rectifiers. The power densities generally used in electrolysis are 250-340 A/m2, and the current is direct current (DC) or so-called periodical reverse current (PRC). Electrolysis is carried out in separate electrolytic cells, where the number of anode-cathode pairs varies from plant to plant, typically between 30 and 80 pairs. The number of electrolytic cells in the plants also differs. Anodes are typically dissolved for 14-21 days, while the cathode cycle is 7-10 days.
Information of the electrolytic process is collected by means of physical and chemical measurements. Conventional measurement parameters are electrolyte temperature, composition, magnitude of electric current and cell voltage. On the basis of the obtained information, conclusions are made regarding the status of the process, and when necessary, control measures are taken for correcting the development of the process status in the right direction.
Real-time monitoring and observation of the status and efficiency of an electrolytic process is challenging, because there are typically hundreds of electrolytic cells in a production plant. Conventionally the process management is based on outdated information and on the observations of process operators. In addition, a lot of manual operations are required of the process operators, mostly due to the process structure and the lack of aiding technologies.
Publication EP 1 239 061 A2 discloses a galvanization plant that comprises an arrangement for indicating the status of groups of cells.
In the publication WO 2005/052700 (Outokumpu Oyj) and in the publication WO 2005/090644 (Kennecott Utah Copper Corporation), there are described methods for creating real-time monitoring systems. For example by these methods, there can be made a calculatory estimate of the real-time status and efficiency of each cell, based on the process estimates measured from the cell, such as cell voltage, electrolyte temperature, electrolyte composition and electric current passing through the cell. Thus, the state of the currently known art is represented by wired and wireless systems that collect information from the process status (for instance of shortcuts occurring in electrolytic cells) and can be observed from a centralized control center/display screen/database/etc.
In the publication WO 2005/052700 (Outokumpu Oyj), there is introduced a method for controlling an electrolytic process and plant, utilizing history data collected in the process as well as mathematical and heuristic models created on the basis of empirical knowledge, and by means of said models, there are defined status indexes as well as alternatively also condition indexes on the basis of real-time measurement parameters from the process. The method makes use of real-time cell voltage and temperature measurements. On the basis of the obtained real-time indexes, there is achieved a correctly focused process control action at the correct point of time. The invention described in the publication WO 2005/052700 has in practice been applied in the CellSense™ control system by Outotec Oyj, said system being a computer program by which for example the operation of single electrolytic cells in an electrolytic plant can be observed cell-specifically, in a centralized way in a control center.
The publication WO 2005/090644 (Kennecott Utah Copper Corporation) introduces an electrolytic cell, monitoring system, a device for monitoring an electrolytic cell and a method for monitoring an electrolytic cell. The invention described in the publication WO 2005/090644 has in practice been applied in the CellSensor™ device of Outotec Oyj, said device being a device for measuring the process parameters in an electrolytic process carried out in an electrolytic cell, and for wirelessly transmitting the measured process parameters to the CellSense™ control system for an analysis of the measured process parameters and for calculating a cell-specific real-time status index for each electrolytic cell included in the system.
A drawback in the CellSense™ control system is that the real-time information describing the electrolytic process, such as a status or condition index, can only be seen on the computer screen, i.e. in the location where the CellSense™ control system is being used and where it is physically located, for instance in the control center of an electrolytic plant, or in a few centralized points of observation in the electrolytic plant. Consequently, corrective or anticipatory measures require that the control center first has detected a problem, and that the detected problem is thereafter communicated to the control center process operator, and only then can the process operator perform the necessary measures for eliminating the problem.
The object of the present invention is to realize an arrangement and method by which process operators can in real time observe the status of an electrolytic process, locally and cell-specifically at individual electrolytic cells of an electrolytic plant, without needing any portable auxiliary devices.